A propeller blade is fixed in a propeller hub by the blade shank, which has means for anchoring in the hub according to a longitudinal axis of the blade, therefore according to a radial axis of the hub. Often, the blade shank comprises an anchoring bushing, which provides a mechanical connection and anchoring in the hub, and a means of fixing to the aerodynamic portion of the blade.
In addition, turbine engine blades are subjected to very considerable forces, so that the assembly of the aerodynamic portion to the blade shank must be sufficiently strong to retain the blade in the hub, transmit the movement of the hub to the blades, and transmit the forces of the blades to the hub (especially propulsion of the aircraft).
The blade shank and more particularly the anchoring bushing and the means of fixing the aerodynamic portion to the blade shank are therefore subjected to high stresses—especially during high acceleration—and to high levels of vibration. Furthermore, they are subject to considerable forces in a continuous and sustained manner during long flights, and to impacts in the event of collisions of a blade with a bird, for example.
In the event of rupture of the assembly of the aerodynamic portion in the blade shank while the propeller is rotating, part of the blade is sometimes freed, which can have serious consequences for the aircraft and its occupants, or for people and buildings on the ground.
U.S. Pat. No. 3,734,642 describes a blade, a spar of which is adhesively bonded between a first tapered sleeve and a second tapered sleeve. The second sleeve is bolted to a hub. In the event of rupture of the connection between the spar and the second sleeve, the spar is retained relative to the hub by means of a shoulder of the first sleeve, which is adapted to cooperate with a shoulder of the second sleeve.
However, the manufacture and mounting of such a blade are complex and therefore lengthy and expensive, because complex adhesive bonding must be carried out between the spar and the sleeves. Furthermore, such a blade is incompatible with modern blades, which generally allow the pitch of the blade to be adjusted in flight. Moreover, the costs and maintenance times of such a blade are high. In fact, inspection or replacement of the aerodynamic portion require the blade to be dismantled completely relative to the hub. In particular, the condition of the portion of the spar that extends into the blade shank cannot be evaluated by non-destructive means.
The invention therefore aims to remedy these disadvantages.